Micro-CT Image Subtraction For Accessing Enamel Demineralization And Remineralization

Objective: We have investigated a new in vitro method to assess demineralization and remineralization of enamel using micro-CT. We aimed at developing an image subtraction technique that will enhance detection and accuracy in measuring mineral change during treatment periods. The method was based on removing with precision the mutual information of pairs of images at different time points.

Methods: Demineralization-group: 4 enamel slabs were subjected to acetic acid solution at pH4.47 for 0h, 24h, 72h and 96h. Remineralization-group: 4 demineralized enamel slabs were treated with fluoride containing remineralizing solution for 8 days. Enamel slabs in the two groups were scanned at different time points using micro-CT. VG-Studio was used to register of the reconstructed volumes at different time points to minimize spatial shifting. Matlab was used to correct image shifting and to subtract image sets to assess mineral change over time (Fig.1A). Finally, mineral loss/restored within the volume of interest was quantified using CT-Analyzer.

Results: Image shifting between two data sets was accurately corrected after image registration (Fig.1B). Image subtraction showed that the volumetric mineral loss after demineralization for 24h, 72h and 96h was 19.6%, 37.9% and 48.7%, respectively. In the Remineralization group subtracted images indicated that the lesions regained 47%, 60.2% and 89% of the total mineral loss after fluoride treatment for 3d, 5d and 8d, respectively. We assessed that our image subtraction technology had higher accuracy than Area-Under-Curve subtraction method.

Conclusions: We have developed a new technique to quantify enamel demin/remineralization based on digital micro-CT with precise image registration followed by image subtraction. The image subtraction enhanced the contrast of the volume of mineral change in the micro-CT scans and improved the quantitative volumetric analysis. Thus, this technique is well adapted for tracking enamel caries lesion development.